1. Field of the Invention
Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for a Boiling Water Reactor (BWR) jet pump main wedge clamp that physically restrains a BWR jet pump main wedge, to prevent wear to the wedge and a jet pump restrainer bracket.
2. Related Art
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends (for example by a bottom head and a removable top head). A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.
In a BWR, hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core water flow. The upper portion of the jet pump, known as the inlet mixer, is laterally positioned and supported against two opposing rigid contacts within jet pump restrainer brackets by a gravity actuated wedge. The restrainer brackets support the inlet mixer by attaching the inlet mixer to the adjacent jet pump riser pipe.
The jet pump main wedge maintains contact between the inlet mixer and the jet pump restrainer bracket. More specifically, the wedge works in cooperation with two set screws which are tack welded to the restrainer bracket to maintain contact with the inlet mixer. The flow of water through the jet pumps typically includes pressure fluctuations caused by various sources in the reactor system. The pressure fluctuations may have frequencies close to one or more natural vibration modes of the jet pump piping. The jet pump piping stability depends on the tight fit-up, or contact, of the restrainer brackets and the inlet mixers. The vibrations present in the jet pump system cause excessive movement of the main wedge against the restrainer bracket and main wedge rod resulting in subsequent damage to the various contact surfaces. Previously worn main wedges and restrainer brackets required replacement and/or new wear surfaces which may be bolted onto the existing restrainer bracket. These procedures have been found to require a significant and expensive downtime of the jet pumps.
Disassembly and/or complete removal of the restraining bracket and wedge can, in and of itself, be expensive. Therefore, a need exists to remove the main wedge from active use by vertically lifting the main wedge away from direct contact with the restraining bracket, thereby allowing the wedge and restrainer bracket to remain attached to the inlet mixer while ensuring that no additional wear occurs between the wedge and the restrainer bracket.